The presidential debate season is upon us with President Obama and his Republican challenger, Mitt Romney, scheduled to square off Wednesday night in the Political Class version of a cage match.

Heading into the debates, the conventional wisdom suggests that Romney has fallen way behind and has to dramatically change the course of the race in these head-to-head events. Some even suggest that the debates are Romney's only chance to bring about a change in the race.

If that's true, Romney's in trouble. The last time a presidential debate changed the race was in 1980, when Ronald Reagan outperformed Jimmy Carter. More recent history shows the debates having only a modest impact.

In 2008, heading into the first debate, Rasmussen Reports polling showed Barack Obama up 50 percent to 45 percent over John McCain. After that debate, the numbers were 51 percent to 45 percent. On Election Day, it was Obama 53 percent, McCain 46 percent. The debate did little for either man.

Four years earlier, there was a similar reaction to the debates between President George W. Bush and John Kerry. When Bush had a bad night, the only thing that changed was Bush supporters decided (after the fact) that debates didn't matter all that much.

So barring a major misstep like President Ford's 1976 assertion that Poland was not under Soviet domination, the upside for either candidate in the 2012 debates is a minor shift in the race. But that may be enough. While national polling has shifted a bit in the president's direction over the past couple of weeks, the candidates remain very close.

In the past couple of elections, the numbers have shifted three points between late September polling and the actual results on Election Day. If they shift that much in Obama's direction, he would enjoy a modestly comfortable victory. If the numbers shift that much in the opposite direction, Romney could emerge victorious.

Any potential change could come from the roughly 10 percent of voters nationwide who currently plan to vote for one of the candidates but could still change their mind. They are roughly evenly split between Obama and Romney, with a slightly larger number currently backing the president. These voters are likely to tune in for the debates and might respond to comments that seem way off-key. If Obama is able to get Romney to respond in a manner that seems out of touch or mean-spirited, that could erode support for the GOP standard-bearer.

On the other hand, if Romney can get Obama to say something suggesting he values government workers more than those in the private sector, that, too, could have an impact. It would be especially harmful for the president if he were to say anything suggesting that Republicans were right in their interpretation of his controversial "you didn't build that" comments.

It's important to keep all of this in context. Events in the real world matter more than the debates. News that changes perceptions of the economy or surprises on the international front could determine the winner. Only in the absence of other news could a slight change in the race coming out of the debates be decisive.

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